Is it addition or subtraction?

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Objective

SWBAT apply properties of operations as strategies to add and subtract.

Big Idea

Addition and subtraction facts are related, and my First Graders need more practice in using properties of operations to make decisions about equations. This lesson has them decide which operation is being completed to make the equation true.

Rev Them Up

5 minutes

I will have my students play a game of "Around the World."

Directions: This is a competitive game to see who can say the correct answer first.  You begin by selecting two students.  These students stand up and you will ask your question.  Whoever says the answer first wins.  The winner is then matched with a new person and the same process proceeds.  You will continue to match the winner with a new person until everyone in the room has a turn and the final winner is produced. I love this game because it can be used in any content area. Go here to see a video of my class playing the game to compare numbers.

Today's lesson will review addition and subtraction and work towards building fluency in solving equations. For this game I will have my students answering questions to increase their fluency with simple addition and subtraction facts. 

Examples:

Okay, here we go, what is the answer to?

2+2=

3-1=

5+6=

Continue with numbers like this until everyone has a turn.

Whole Group Interaction

10 minutes

I have taught many lessons for my students to see the relationship between numbers and identify how using this relationship can help them solve equations. This lesson will encourage my students to use counting strategies such as counting all, counting on, and counting back. (1.OA.C.5). This concept is introduced by using unifix cubes to show students the part-part-whole relationship occurring in an equation. Eventually they are able to use ten as a benchmark number and this counting strategy will go to the way side, but for now these counting strategies assist them identifying whether numbers are being added together or being subtracted. I want them to be thoughtful problem solvers, and allow them the opportunity to attack a problem from a different angle.

I will open up this Smartboard image and pose the question, "what kind of math are we doing for the first equation to be true?"

We will go through each problem in the image and decide if it is addition or subtraction. The most important thing is to ask questions for them to explain their thinking and have a class discussion about each problem:

  • How do you know it is addition/subtraction?  (I can take two cubes and add 3 cubes to it and have 5 total. If I have 5 cubes and count back two cubes, I will have 3 cubes leftover.)
  • What hints are in the problem that helped you figure it out? (Because the answer it greater than the first number, so it is addition. It said 2 blank 3 equals 5 and I know if I start at 2 and count up 3,4, then 5 is the answer.) 

Discussions about math improve my students ability to clearly and concisely express their mathematical ideas and critique the ideas of others. (MP3). Help for concrete learners: You may have some students who struggle with seeing the part, part, whole relationship. If so, get unifix cubes out and show them the whole amount, then help them see the two parts. For example, if the answer is 7, show them that, then break it into 3 and 4, and ask, will I need to join the 3 and 4 together to get 7 or am I taking them apart to get 7? Students should see they needed to be added together to get 7. For a subtraction example, you might start with 5 cubes and ask students what would you need to do to have the answer 3? You walk them through the thought process to get to taking 2 away, and naming the problem as subtraction.

Independent Practice

15 minutes

Print the Subtraction or addition worksheet and copy for each student. I have shown my students how to solve these problems by manipulating cubes and determining if we are adding parts together to reach the final answer or taking parts away to gain the final answer. Some students may need to use manipulatives to solve their problems. I will be walking around and assisting students who are still using the concrete method to solve. I am hoping to find some students who identify the relationship between the numbers and transition from using the manipulatives to solving on their own.

You can view work examples here and note how one student discovered early on that one of the problems can be plus or minus as the answer.  I hate it when I cannot catch everything in a video, but I had more than one student identifying that the same problem that could be plus or minus. I asked them to explain how they knew and they immediately talked about Zero the Hero, which is our way of making the Identity Property (that any number added to zero is the same number and any number with zero subtracted from it is the same number) fun. 

Closing

5 minutes

Pass out a sheet of handwriting paper for them to explain their answer in words. Write these two problems on the board;

13 __ 0= 13      0__ 13= 13 

Then ask:

Can both of these problems be plus and minus? How do you know?